1. Field of the Invention
The present disclosure relates to a measuring system and, in particular, to a measuring system for measuring a physical quantity of electromagnetic wave or magnetism in a magnetic shield room.
2. Description of the Related Art
In recent years, much research of medical robotic instruments, such as a manipulator, has been reported. A typical example of a medical robotic instrument is a medical system using a magnetic resonance imaging (MRI) apparatus. In the medical system, an MR image is viewed and the position of a robot arm of a manipulator is controlled in order to diagnose with an accurate biopsy and provide medical treatment. An MRI system is a measuring system in which an electromagnetic wave generated by a static magnetic field and a particular high frequency magnetic field is applied to a part of an examinee (an object to be examined) and, thereafter, by using nuclear magnetic resonance occurring in the object to be examined, an image of the specimen is generated. In this manner, the MRI system acquires information regarding the object to be examined.
Since an MRI system uses a strong magnetic field, it is difficult to use an electromagnetic motor that includes a ferromagnetic material as a power source of a robot arm. Accordingly, a vibration-type actuator, such as an ultrasonic motor, is suitable for the power source. However, since high-frequency noise generated by a control unit of the vibration-type actuator also has an impact on an MR image, the noise generated by the control unit needs to be minimized or shielded. In general, a central processing unit (CPU) or a field programmable gate array (FPGA) that serves as the control unit operates with an external clock of about 10 MHz to about 50 MHz. Accordingly, high-frequency noise generated by the clock signal is transferred to the vibration-type actuator via, for example, a driving waveform signal and, thus, electromagnetic noise is generated around the vibration-type actuator.
Japanese Patent Laid-Open No. 2011-245202 describes a configuration in which the vibration-type actuator is disposed in a cylindrical measuring unit (a bore) of an MRI apparatus while a control unit of the vibration-type actuator is disposed at a position that is the furthest away from the measuring unit of the MRI apparatus placed in a magnetic shield room. In addition, the vibration-type actuator is connected to the control unit using an electromagnetically shielded control line.
Another configuration is described in “Basic Contract Accomplishment Report of Research and Development of Miniature Surgical Robotic System Achieving Future Medical Treatment,”, New Energy and Industrial Technology Development Organization. In the configuration, a control unit and a drive circuit of the vibration-type actuator are disposed outside a magnetic shield room and are connected to the vibration-type actuator disposed in the magnetic shield room using a double-shielded electric cable. In addition, a noise filter is provided to part of the cable that passes through a wall of the magnetic shield room to block noise getting into the magnetic shield room. Furthermore, in order to reduce electromagnetic noise generated by an electric current flowing in the vibration-type actuator, the vibration-type actuator is disposed in an aluminum case so as to be electromagnetically shielded.
In Japanese Patent Laid-Open No. 2011-245202, the vibration-type actuator is connected to the control unit using a shielded line. However, since the control unit is disposed in the magnetic shield room, high-frequency radiation noise from the control unit may have an impact on an MR image. In addition, in the technique described in “MRI-compatible Compact Surgical Robot Master-Agreement Research Report”, the electric cable extending to the vibration-type actuator is double-shielded, and a connection port connected to the magnetic shield room has a noise filter. However, since the vibration-type actuator is electrically connected to the drive circuit and the control unit, it is difficult to completely block high-frequency noise. Accordingly, if the vibration-type actuator is driven in the vicinity of the MRI apparatus, noise may be coupled into an MR image. In addition, as the length of the interconnection line of the vibration-type actuator increases, the load capacity of the interconnection line increases and, therefore, power consumption may increase.